Personal video recording is a new digital technology in which a video stream is recorded on a medium such as a hard drive. In its most common form, an MPEG2 video steam is decoded. The decoder may be included in a digital television, a cable/satellite set top box or personal video recorder. “Trick-mode” refers to such functions as pause, rewind and slow-motion. The trick is that these modes may be applied to a live broadcast. The illusion of pausing a live broadcast is given by continuing to record a broadcast after a pause button is activated and playing the recording back on command. Trick-mode operation is achieved by playback of a video stream called the “trick-mode stream” on the decoding device. A trick-mode stream can be created in different ways. The speed of response and picture quality in utilization of the trick-mode stream will be functions of the manner in which the stream is created. Two different ways of creating the trick mode stream are the most prevalent.
One form of video stream creation is based on a look-up table. During recording of the stream, a table is created which contains pointers to various information in headers each associated with a video signal payload. A table is assembled which can point to headers for a Group of Pictures (GOP), sequence or picture. This table is used to assemble the trick-mode stream during trick-mode playback. Headers are selected in correspondence with the particular trick-mode that is commanded. Implementing this form of recording requires software that provides extensive CPU intervention during the recording process in order to parse the video stream and select header information to generate the pointer table. More recently, in the alternative, specialized hardware modules have been developed to implement the algorithms for generating the look-up tables.
Another prevalent way of creating the trick-mode stream is concatenating segments of a full-recorded stream. Selection of segments is based on heuristic criteria. For example, at initiation of playback, hardware could select segments of the recorded stream at each new sector of the storage device. This method is fast and simple. However, the frames accessed while producing the trick-mode stream may be partial in some cases rather than complete. Including partial frames in the trick-mode stream causes presentation of undesirable video artifacts in the playback display.